Physical quantity sensor module, clinometer, and structure monitoring device

ABSTRACT

A physical quantity sensor module includes: a resonant frequency shift based physical quantity sensor whose frequency adjusts with a adjust in physical quantity; a reference signal oscillator which outputs a reference signal; a frequency delta-sigma modulator which performs frequency delta-sigma modulation of the reference signal, using an operation signal based on a measurement target signal as an output from the resonant frequency shift based physical quantity sensor, and generates a frequency delta-sigma modulated signal; a first low-pass filter provided on an output side of the frequency delta-sigma modulator and operating synchronously with the measurement target signal as the output from the resonant frequency shift based physical quantity sensor; and a second low-pass filter provided on an output side of the first low-pass filter and operating synchronously with the reference signal.

The present application is based on, and claims priority from JapaneseApplication Serial Number 2018-081177, filed Apr. 20, 2018, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a physical quantity sensor module andthe like.

2. Related Art

A physical quantity sensor forming a physical quantity sensor module fordetecting a physical quantity such as acceleration has a problem ofnonlinearity in that the relation between the physical quantity and theoutput value is not linear. To correct this nonlinearity, for example,providing a nonlinearity correction circuit for changing the degree ofamplification of output for an electrostatic capacitance-type physicalquantity sensor, which is a type of physical quantity sensor and whichdetects an acceleration, is known. JP-A-9-33563 is an example of therelated art.

However, providing a dedicated circuit or a dedicated mechanism such asproviding a nonlinearity correction circuit has a problem in that itincreases the circuit scale of the physical quantity sensor module andconsequently increases the cost.

SUMMARY

An advantage of some aspects of the present disclosure is to solve atleast a part of the foregoing problem and the present disclosure can beimplemented as the following configurations or application examples.

A first aspect of the disclosure is directed to a physical quantitysensor module including: a resonant frequency shift based physicalquantity sensor whose frequency adjusts with a adjust in physicalquantity; a reference signal oscillator which outputs a referencesignal; a frequency delta-sigma modulator which performs frequencydelta-sigma modulation of the reference signal, using an operationsignal based on a measurement target signal outputted from the resonantfrequency shift based physical quantity sensor, and generates afrequency delta-sigma modulated signal; a first filter provided at anoutput of the frequency delta-sigma modulator and operatingsynchronously with the measurement target signal; a second filterprovided on an output side of the first filter and operatingsynchronously with the reference signal; and a latch provided betweenthe first filter and the second filter and operating synchronously withthe reference signal. The resonant frequency shift based physicalquantity sensor has nonlinearity as a characteristic of an output signalto the physical quantity.

According to the first aspect, the filter provided on the output side ofthe frequency delta-sigma modulator includes a combination of the firstfilter operating synchronously with the measurement target signal as anoutput from the resonant frequency shift based physical quantity sensor,and the second filter operating synchronously with the reference signal.This enables correction of the nonlinearity of the measurement targetsignal. Therefore, a dedicated circuit or a dedicated mechanism such asa nonlinearity correction circuit need not be provided. Thus, thenonlinearity of the measurement target signal outputted from thephysical quantity sensor can be corrected without increasing the size ofthe physical quantity sensor module and with a low cost.

A second aspect of the disclosure is directed to the physical quantitysensor module according to the first aspect, in which a cutoff frequencywhich is a filter characteristic achieved by a combination of the firstfilter and the second filter is lower than a structure resonancefrequency of the resonant frequency shift based physical quantitysensor.

According to the second aspect, the first filter and the second filtercan reduce a noise component resulting from the structure resonancefrequency where a vibration rectification error emerges prominently.

A third aspect of the disclosure is directed to the physical quantitysensor module according to the second aspect, in which the structureresonance frequency is a frequency determined based on a structure ofthe resonant frequency shift based physical quantity sensor.

According to the third aspect, the structure resonance frequency can bedetermined based on the structure of the resonant frequency shift basedphysical quantity sensor.

A fourth aspect of the disclosure is directed to the physical quantitysensor module according to one of the first to third aspects, in whichthe first filter has an input/output characteristic set in such a waythat the nonlinearity of the measurement target signal as the outputfrom the resonant frequency shift based physical quantity sensor becomescloser to linearity.

According to the fourth aspect, the measurement target signal as theoutput from the resonant frequency shift based physical quantity sensoris passed through the first filter and the nonlinearity of themeasurement target signal is thus corrected to become closer tolinearity. The resulting signal is used as the output from the physicalquantity sensor module.

A fifth aspect of the disclosure is directed to the physical quantitysensor module according to the fourth aspect, in which the first filteris a smoothing filter configured to adjust a smoothing timing based on anumber of filter taps, and the number of filter taps is set to asmoothing timing that reduces a vibration rectification error of themeasurement target signal as the output from the resonant frequencyshift based physical quantity sensor emerging due to the nonlinearity.

According to the fifth aspect, the smoothing timing of the first filteras the smoothing filter is adjusted by the number of filter taps. Thisreduces the vibration rectification error of the measurement targetsignal as the output from the resonant frequency shift based physicalquantity sensor. Thus, the nonlinearity of the measurement target signalcan be corrected.

A sixth aspect of the disclosure is directed to the physical quantitysensor module according to the fifth aspect, in which a setting of thenumber of filter taps is adjustable from outside.

According to the sixth aspect, the setting of the number of filter tapsof the first filter is adjustable from outside. Therefore, for eachphysical quantity sensor module, the number of filter taps of the firstfilter can be properly set or reset according to the characteristic ofthe resonant frequency shift based physical quantity sensor.

A seventh aspect of the disclosure is directed to the physical quantitysensor module according to the fifth or sixth aspect, in which the firstfilter is configured to adjust the smoothing timing based on a pluralityof numbers of filter taps with different levels of roughness/fineness ofan amount of adjust in the smoothing timing.

According to the seventh aspect, the plurality of numbers of filter tapswith different levels of roughness/fineness of the amount of adjust inthe smoothing timing makes it easy to adjust the degree of correction ofthe nonlinearity of the measurement target signal as the output from theresonant frequency shift based physical quantity sensor.

An eighth aspect of the disclosure is directed to the physical quantitysensor module according to one of the first to fifth aspects, in whichthe physical quantity is acceleration.

According to the eighth aspect, the physical quantity sensor modulewhich detects an acceleration can achieve the advantageous effects ofthe first to fifth aspects.

A ninth aspect of the disclosure is directed to a clinometer including:the physical quantity sensor module according to the eighth aspect; anda calculator which calculates an angle of inclination based on an outputfrom the physical quantity sensor module.

According to the ninth aspect, a clinometer with a higher accuracy ofcalculation of the angle of inclination than in the related art can beachieved.

A tenth aspect of the disclosure is directed to an inertial measurementdevice equipped on a vehicle including: the physical quantity sensormodule according to the eighth aspect; an angular velocity physicalquantity sensor module; and a circuitry which calculates an attitude ofthe vehicle, based on an output from the physical quantity sensor moduleand an output from the angular velocity physical quantity sensor module.

According to the tenth aspect, an inertial measurement device with ahigher accuracy of calculation of the attitude of the vehicle than inthe related art can be achieved.

An eleventh aspect of the disclosure is directed to a structuremonitoring device including: the physical quantity sensor moduleaccording to the eighth aspect equipped on a structure; a transmitterwhich is equipped on the structure and transmits an output from thephysical quantity sensor module; a receiver which receives a signaltransmitted from the transmitter; and a calculator which calculates anangle of inclination of the structure, based on a signal received by thereceiver.

According to the eleventh aspect, a structure monitoring device with ahigher accuracy of calculation of the angle of inclination of thestructure than in the related art can be achieved.

A twelfth aspect of the disclosure is directed to a vehicle including:the physical quantity sensor module according to the eighth aspect; anda controller which controls at least one of acceleration, braking, andsteering, based on an output signal from the physical quantity sensormodule. Whether to execute automatic driving or not is switched, basedon an output from the physical quantity sensor module.

According to the twelfth aspect, a vehicle with higher quality ofautomatic driving than in the related art can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a physicalquantity sensor module according to a first embodiment.

FIG. 2 is an explanatory view of vibration rectification error.

FIG. 3 is an explanatory view of structure resonance frequency.

FIG. 4 is a block diagram showing the configuration of a first low-passfilter in the first embodiment.

FIG. 5 is a block diagram showing the configuration of a second low-passfilter in the first embodiment.

FIG. 6 is an explanatory view of nonlinearity in the first embodiment.

FIG. 7 shows an example of an experiment result in the first embodiment.

FIG. 8 is a schematic cross-sectional view of a physical quantitydetector according to a second embodiment.

FIG. 9 is a schematic perspective view of a physical quantity detectiondevice in the second embodiment.

FIG. 10 is a schematic perspective view of the physical quantitydetection device in the second embodiment.

FIG. 11 is a plan view of the physical quantity detection device in thesecond embodiment.

FIG. 12 shows the configuration of an acceleration physical quantitysensor according to a third embodiment.

FIG. 13 is a schematic cross-sectional view of a clinometer according toa fourth embodiment.

FIG. 14 is a schematic cross-sectional view of an inertial measurementdevice according to a fifth embodiment.

FIG. 15 is a schematic view showing the configuration of a structuremonitoring device according to a sixth embodiment.

FIG. 16 is a schematic view showing the configuration of a vehicleaccording to a seventh embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Suitable embodiments of the disclosure will now be described withreference to the drawings. However, the following embodiments should notlimit the disclosure and should not limit any form to which thedisclosure is applicable.

First Embodiment

Configuration

FIG. 1 is a block diagram showing the configuration of a physicalquantity sensor module 1 according to a first embodiment. As shown inFIG. 1, the physical quantity sensor module 1 has a resonant frequencyshift based physical quantity sensor 3, a reference signal oscillator 5,and a frequency ratio measuring device 7. The resonant frequency shiftbased physical quantity sensor 3 is a physical quantity sensor whosefrequency adjusts according to an adjust in a detection target physicalquantity. The resonant frequency shift based physical quantity sensor 3outputs a periodic signal corresponding to the frequency, as ameasurement target signal. The resonant frequency shift based physicalquantity sensor 3 may be, for example, a quartz crystal velocityphysical quantity sensor which measures an acceleration as a physicalquantity, or may be a quartz crystal angular velocity physical quantitysensor which measures an angular velocity as a physical quantity. Thereference signal oscillator 5 outputs a reference signal based on apredetermined frequency. The frequency of the reference signal is higherthan the frequency of the measurement target signal.

The frequency ratio measuring device 7 is a device which measures thefrequency ratio between the measurement target signal and the referencesignal, based on the measurement target signal and the reference signal.The frequency ratio measuring device 7 measures the frequency ratio by areciprocal counting method. Instead of the measurement target signal, anoperation signal based on the measurement target signal may be used. Theoperation signal based on the measurement target signal is a signalcorrelated with the measurement target signal and includes themeasurement target signal itself. The frequency ratio measuring device 7has a frequency delta-sigma modulator 10, a first low-pass filter 20, athird latch 50, and a second low-pass filter 60.

The frequency delta-sigma modulator 10 performs frequency delta-sigmamodulation of the reference signal outputted from the reference signaloscillator 5, using the measurement target signal as the output from theresonant frequency shift based physical quantity sensor 3, and generatesa frequency delta-sigma modulated signal. The frequency delta-sigmamodulator 10 has a counter 12, a first latch 14, a second latch 16, anda subtractor 18. The counter 12 counts a rising edge of the referencesignal and outputs count data representing a count value. The firstlatch 14 latches the count data and outputs first data, synchronouslywith a rising edge of the measurement target signal. The second latch 16latches the first data and outputs second data, synchronously with therising edge of the measurement target signal. The subtractor 18subtracts the second data from the first data and generates output data.This output is the frequency delta-sigma modulated signal generated bythe frequency delta-sigma modulator 10.

The frequency delta-sigma modulator 10 is also called a first-orderfrequency delta-sigma modulator. The frequency delta-sigma modulator 10latches the count value of the reference signal twice by the measurementtarget signal and sequentially holds the count value of the referencesignal, triggered by the rising edge of the measurement target signal.Although it is assumed in this example that the latch operation iscarried out at the rising edge, the latch operation may be carried outat a falling edge or both at the rising edge and at the falling edge.The subtractor 18 calculates the difference between the two count valuesthus held, and outputs an increase in the count value of the referencesignal observed during a one-period transition of the measurement targetsignal, without any dead time with the lapse of time. The frequencyratio is fc/fx, where fx is the frequency of the measurement targetsignal and fc is the frequency of the reference signal. The frequencydelta-sigma modulator 10 outputs the frequency delta-sigma modulatedsignal representing the frequency ratio, as a digital signal string.

The first low-pass filter 20 is an example of a first filter and isprovided on the output side of the frequency delta-sigma modulator 10.The first low-pass filter 20 operates synchronously with the measurementtarget signal as the output from the resonant frequency shift basedphysical quantity sensor 3 and eliminates or reduces a noise componentincluded in the frequency delta-sigma modulated signal outputted fromthe frequency ratio measuring device 7.

The third latch 50 latches and outputs the output from the firstlow-pass filter 20 synchronously with the rising edge of the referencesignal.

The second low-pass filter 60 is an example of a second filter and isprovided on the output side of the first low-pass filter 20, which is anexample of the first filter. The second low-pass filter 60 operatessynchronously with the reference signal and eliminates or reduces anoise component included in the frequency delta-sigma modulated signaloutputted from the frequency ratio measuring device 7.

Principles

The frequency ratio measuring device 7 in this embodiment corrects thenonlinearity of the measurement target signal as the output from theresonant frequency shift based physical quantity sensor 3. If theresonant frequency shift based physical quantity sensor 3 is, forexample, a quartz crystal acceleration physical quantity sensor, theresonant frequency shift based physical quantity sensor 3 is a physicalquantity sensor utilizing a adjust in the oscillation frequency(vibration frequency) of a quartz crystal vibrator corresponding to aadjust in a force acting along a detection axis. The resonant frequencyshift based physical quantity sensor 3 outputs a signal changing in apulse-like form corresponding to the oscillation frequency. The relationbetween the acting acceleration and the oscillation frequency of thequartz crystal vibrator is not perfectly linear (nonlinear). Therelation varies from one sensor to another.

FIG. 2 is a schematic view for explaining the way a drift occurs in a DCcomponent of an output value when a vibration component is inputted to asystem having a nonlinear input/output relation. Inputting a sinusoidalsignal to a system having a linear input/output relation results in anoutput value indicated by a solid curve in FIG. 2. No drift occurs in aDC component (solid straight line) obtained by rectifying this outputvalue. Meanwhile, inputting a sinusoidal signal to a system having anonlinear input/output relation results in an output value indicated bya dashed curve in FIG. 2. Adrift due to a distortion of output waveformoccurs in a DC component (dashed straight line) obtained by rectifyingthis output value. The drift component generated in the output when avibration component is inputted to the system having the nonlinearinput/output relation is called a vibration rectification error (VRE).Generally, the VRE is a function of the frequency of the inputtedvibration component. It is known that the magnitude of the VRE isproportionate to the square of the amplitude of the inputted vibrationcomponent, provided that the frequency of the inputted vibrationcomponent is constant.

FIG. 3 shows a vibration rectification error constant (VRC) traced as afunction of the application frequency of applied acceleration in thepre-adjustment physical quantity sensor module 1 configured to detect anacceleration. Since the magnitude of the VRE is proportionate to thesquare of the amplitude of the inputted vibration component, the VRC inthe physical quantity sensor module configured to detect an accelerationis expressed in [G/G{circumflex over ( )}2]. A VRC peak observed near820 Hz has a value greater by four to five digits than in the otherfrequency regions. This is due to the following reason. That is, thestructure resonance frequency of structure resonance determined by thestructure of the physical quantity sensor module is approximately 820Hz, and a frequency of approximately 820 Hz, if included in the inputtedvibration component, causes structure resonance of the physical quantitysensor module. Thus, apparently, the frequency component correspondingto the structure resonance frequency is amplified and outputted.Consequently, a drift due to the structure resonance contributes most tothe VRE. Thus, a special countermeasure is needed.

The frequency ratio measuring device 7 corrects the measurement targetsignal as the output from the resonant frequency shift based physicalquantity sensor 3 having nonlinearity. The frequency ratio measuringdevice 7 particularly reduces the VRE due to the structure resonance andthus can reduce the nonlinearity between the acceleration acting on theresonant frequency shift based physical quantity sensor 3 and the outputfrom the frequency ratio measuring device 7.

FIG. 4 is a block diagram showing the configuration of the firstlow-pass filter 20. As shown in FIG. 4, the first low-pass filter 20 hasa first adder 22, a first delay element 24, a first subtractor 26, asecond adder 28, a third adder 30, a decimator 32, a second delayelement 34, a second subtractor 36, a third delay element 38, and athird subtractor 40. Each part of the first low-pass filter 20 operatessynchronously with the measurement target signal. The setting of thenumbers of delays n1 to n3 of the first delay element 24, the seconddelay element 34, and the third delay element 38, respectively, as thenumbers of filter taps, can be adjusted from outside the physicalquantity sensor module 1. Of the components of the first low-pass filter20, a first section made up of the first adder 22, the first delayelement 24, and the first subtractor 26 functions as a moving averagefilter. Of the components of the first low-pass filter 20, a secondsection made up of the second adder 28, the third adder 30, thedecimator 32, the second delay element 34, the second subtractor 36, thethird delay element 38, and the third subtractor 40 function as acascaded integrator-comb (CIC) filter.

FIG. 5 is a block diagram showing the configuration of the secondlow-pass filter 60. As shown in FIG. 5, the second low-pass filter 60has a fourth adder 62, a fourth delay element 64, and a fourthsubtractor 66. Each part of the second low-pass filter 60 operatessynchronously with the reference signal. The setting of the number ofdelays n4 of the fourth delay element 64, as the number of filter taps,can be adjusted from outside the physical quantity sensor module 1. Thesecond low-pass filter 60 functions as a moving average filter.

The setting of the numbers of filter taps n1 to n3 of the first low-passfilter 20 and the number of filter taps n4 of the second low-pass filter60 thus configured realizes the nonlinearity of the input/outputcharacteristic of the frequency ratio measuring device 7. Specifically,based on a characteristic such that the phase of an output is delayed by(n1−1+R×(n2+n3−1))/2 clocks from an input to the first low-pass filter20 operating based on the measurement target signal, where R is thedecimation ratio of the CIC filter, and by taking out and smoothing theoutput from the first low-pass filter 20 by the number of samples n4 viathe second low-pass filter 60 operating based on the reference signal,the nonlinearity of the input/output characteristic is realized. Thefirst low-pass filter 20 functions as a cascaded moving average filterand the second low-pass filter 60 functions as a moving average filter,thus smoothing and outputting an input signal. In the first low-passfilter 20 and the second low-pass filter 60, changing the numbers ofdelays n1 to n4 of the receptive delay elements can adjust the cutofffrequency and the smoothing timing. The cutoff frequency achieved by acombination of the first low-pass filter 20 and the second low-passfilter 60, of the resonant frequency shift based physical quantitysensor 3, is prescribed to be lower than the structure resonancefrequency of the resonant frequency shift based physical quantity sensor3. Therefore, the influence of the structure resonance on outputmodulation can be reduced.

FIG. 6 is a schematic view for explaining a principle on how thefrequency ratio measuring device 7 shows nonlinearity (vibrationrectification error) to a vibration input, due to the input/outputcharacteristic based on the first low-pass filter 20 and the secondlow-pass filter 60. In sections (1) to (3) of FIG. 6 relating tofrequency, time passes as it goes to the right on the sheet, and thereference signal, the measurement target signal, and the sampling signalare shown in order from the top. For the reference signal and themeasurement target signal, the timing of a rising edge is indicated by ashort vertical line. For the measurement target signal, a numeric valuerepresenting the output signal of the first low-pass filter 20 operatingat the timing of the rising edge of the measurement target signal isalso written between the timings of the receptive rising edges. For thesake of convenience of qualitative explanation, the reference signal,the measurement target signal, and the sampling signal are illustratedin such a way that the frequencies (periods) of these signals form asimple ratio, and an input value where only the phase difference isvaried is illustrated as a first low-pass filter output value. However,in the description below, it should be noted that a similar explanationcan be given even when an arbitrary first low-pass filter output valueis used in an arbitrary frequency ratio.

The sampling signal is a signal outputted from the second low-passfilter 60. The second low-pass filter 60 takes in, at the timing of therising edge of the reference signal, the output signal from the firstlow-pass filter 20 via the third latch 50 similarly operatingsynchronously with the reference signal, and outputs the result ofsmoothing. In FIG. 6, focusing on one operation timing t1, a start pointand an end point of a smoothing period are indicated by a short verticalline, and a numeric value representing an output signal is shown alongwith the progress of smoothing. The length of the smoothing period isdetermined by a clock period based on the reference signal, and thenumber of delays n4 of the fourth delay element 64 of the secondlow-pass filter 60.

The first low-pass filter 20 takes in the output signal from thefrequency delta-sigma modulator 10 at the timing of the rising edge ofthe measurement target signal and outputs the result of smoothing. Thefrequency delta-sigma modulated signal as the output signal from thefrequency delta-sigma modulator 10 is the frequency ratio fc/fx betweenthe frequency fx of the measurement target signal and the frequency fcof the reference signal. That is, the first low-pass filter 20 carriesout smoothing of the frequency ratio fc/fx between the measurementtarget signal and the reference signal. The length of the smoothingperiod and the amount of delay are determined by a clock period based onthe measurement target signal, and the numbers of delays n1, n2, and n3of the first delay element 24, the second delay element 34, and thethird delay element 38 of the first low-pass filter 20.

The part (1) of FIG. 6 shows an example where the ratio (reciprocalcount value) between the frequency fc of the reference signal and thefrequency fx of the measurement target signal inputted to the frequencyratio measuring device 7 is a constant integer value. If the ratiobetween fc and fx is a constant integer value, the result of smoothingby the first low-pass filter 20 is a constant value corresponding to thefrequency fx of the measurement target signal. For the sake ofconvenience of the description, in the part (1) of FIG. 6, the number ofrising edges of the reference signal included between the timings ofrising edges of the measurement target signal, “4”, is shown as anumeric value representing the output signal.

The second low-pass filter 60 takes in the output signal from the firstlow-pass filter 20 at the rising timing of the reference signal andoutputs the result of smoothing. In FIG. 6, a value obtained simply byaccumulating values taken in during the smoothing period is shown as theresult of smoothing by the second low-pass filter 60. The samplingsignal in this example is “64”.

The part (2) of FIG. 6, unlike the part (1) of FIG. 6, shows an examplewhere the measurement target signal is FM (frequency modulation)modulated while the total sum of reciprocal count values in therepetition section of the measurement target signal is maintained, andwhere the numbers of delays n1, n2, and n3 of the first delay element24, the second delay element 34, and the third delay element 38 of thefirst low-pass filter 20 are subsequently adjusted in such a way thatthe input and the output are in phase. Due to FM modulation, the timingof the rising edge of the measurement target signal periodically adjustsand the output value from the first low-pass filter 20 as the result ofsmoothing periodically adjusts, too. In the part (2) of FIG. 6, thereciprocal count value, too, adjusts to “5” or “3”. Since the secondlow-pass filter 60 accumulates “5” or “3” based on the reference signal,the reciprocal count value is weighted according to timing. In the part(2) of FIG. 6, the input and the output are adjusted to be in phase.Therefore, the greater the reciprocal count value is, the more it isweighted. The sampling signal in this example is “68”.

The part (3) of FIG. 6 shows an example where the numbers of delays n1,n2, and n3 of the first delay element 24, the second delay element 34,and the third delay element 38 of the first low-pass filter 20 areadjusted in such a way that the input and the output are of the oppositephases, when the measurement target signal is FM-modulated as in thepart (2) of FIG. 6.

Similarly to the part (2) of FIG. 6, the timing of the rising edge ofthe measurement target signal periodically adjusts due to FM modulation,and the output value from the first low-pass filter 20 as the result ofsmoothing periodically adjusts, too. In the part (3) of FIG. 6, thereciprocal count value, too, adjusts to “5” or “3” but of the oppositephase to the part (2) of FIG. 6. Again, the second low-pass filter 60accumulates “5” or “3” based on the reference signal and therefore thereciprocal count value is weighted according to timing. However, in thepart (3) of FIG. 6, the input and the output are adjusted to be of theopposite phases. Therefore, the smaller the reciprocal count value is,the more it is weighted. The sampling signal in this example is “60”.

Generally, FM (frequency modulation) modulating the measurement targetsignal and then adjusting the phase of the input and the phase of theoutput can control the amount of drift of the DC component of thesampling signal as the output from the second low-pass filter. In theexample of FIG. 6, the sampling signal without any drift is “64”, andthe sampling signal can be adjusted to “68” (the amount of drift beingthe maximum “+4”) by bringing the input and the output of the firstlow-pass filter into phase, and “60” (the amount of drift being theminimum “−4”) by bringing the input and the output of the first low-passfilter into the opposite phases. Also, adjusting the phase in the firstlow-pass filter can control the amount of drift to an intermediate valuebetween these values.

Based on the foregoing mechanism, providing a mechanism for adjustingthe output timing of the first low-pass filter can adjust the outputsignal from the second low-pass filter 60. Therefore, the amount ofdrift can be controlled without changing the cutoff frequency.

When the frequency (period) of the measurement target signal does notadjust, as shown in the part (1) of FIG. 6, even though the outputtiming of the first low-pass filter 20 is delayed, the length of thesmoothing period by the first low-pass filter 20 and the result of thesmoothing are not adjusted by the output timing and therefore the outputfrom the second low-pass filter 60 does not adjust.

Changing the setting of the numbers of delays n2 and n3 of the seconddelay element 34 and the third delay element 38 of the first low-passfilter 20 in this way can delay the output timing of the first low-passfilter 20. Thus, the input/output characteristic, which is the relationbetween the frequency of the measurement target signal inputted to thefrequency ratio measuring device 7 and the frequency of the outputsignal, shows nonlinearity and the amount of drift can thus becontrolled.

In the foregoing example, the amount of drift (0→±4) is discussed on theassumption that the measurement target signal is FM (frequencymodulation) modulated (reciprocal count value being 4, 4, 4, 4, →5, 5,3, 3) while the total sum of reciprocal count values in the repetitionsection of the measurement target signal is maintained. However, whenthe amount of FM modulation is doubled (reciprocal count value being 4,4, 4, 4, →6, 6, 2, 2), the amount of drift is 0→±16. Thus, it can beunderstood that the amount of drift is proportionate to the square ofthe amount of FM modulation. Meanwhile, when the frequency of theinputted vibration component is constant, the magnitude of the vibrationrectification error in the output from the resonant frequency shiftbased physical quantity sensor 3 is proportionate to the square of theamplitude of the inputted vibration component. Therefore, adjusting theamount of drift to cancel the vibration rectification error can bringthe input/output relation of the physical quantity sensor module 1 closeto linearity.

Experiment Result

Next, the result of an experiment on the physical quantity sensor module1 will be described. FIG. 7 shows an example of the result of theexperiment. In FIG. 7, the horizontal axis represents time and thevertical axis represents acceleration, and an output from the frequencyratio measuring device 7 when a vibration and hence an acceleration isinstantaneously applied to the resonant frequency shift based physicalquantity sensor 3, is shown. When an acceleration is applied to theresonant frequency shift based physical quantity sensor 3, theoscillation frequency of the resonant frequency shift based physicalquantity sensor 3 adjusts and a signal representing the oscillationfrequency is outputted from the frequency ratio measuring device 7. Thisoutput is equivalent to a detection value of the acceleration by thephysical quantity sensor module 1.

FIG. 7 also shows two cases with different input/output characteristicsof the frequency ratio measuring device 7. The top of FIG. 7 shows theresult of measuring the output from the physical quantity sensor module1 before the adjustment of the input/output characteristic of the firstlow-pass filter. The bottom of FIG. 7 shows the result of measuring theoutput from the physical quantity sensor module 1 after the adjustmentof the input/output characteristic of the first low-pass filter.

In both cases, an impact is applied in such a way that an accelerationis applied like an impulse at a timing of approximately 0.05 seconds.When an acceleration is applied to the resonant frequency shift basedphysical quantity sensor 3, an acceleration as a detection value of thephysical quantity sensor module 1 adjusts. In both cases, thisacceleration (detection value) adjusts with large amplitude and thengradually dies down. However, since the impulse waveform includes abroad range of frequency components, structure resonance is excited aswell. The median of vibration immediately after the timing when theacceleration is applied (immediately after the vibration is applied)varies. That is, the output from the physical quantity sensor module 1before the adjustment of the input/output characteristic of the firstlow-pass filter shown at the top of FIG. 7, the median of vibrationdrifts from the initial value immediately after the vibration isapplied. The amount of this drift Δ (in FIG. 7, approximately 200 mG) isthe vibration rectification error. The drift decreases as the median ofvibration becomes closer to the initial value with the lapse of time.However, it is observed that the median is still not back to the initialvalue, at a point of 0.4 seconds at the right end of the graph.

Meanwhile, in the output from the physical quantity sensor module 1after the adjustment of the input/output characteristic of the firstlow-pass filter shown at the bottom of FIG. 7, the median of vibrationimmediately after the vibration is applied is instantly converged intothe initial value. It can be said that the drift component is reduced.That is, it can be said that the input/output characteristic, which isthe relation between the frequency of the measurement target signalinputted to the frequency ratio measuring device 7 and the frequency ofthe output signal, shows nonlinearity and the amount of drift is thuscontrolled, thereby correcting the vibration rectification error.

Advantageous Effects

According to the first embodiment, changing the setting of the numbersof delays n1 to n4 as the numbers of filter taps of the first low-passfilter 20 and the second low-pass filter 60 can achieve so-called“reverse (line symmetry)” nonlinearity of the input/outputcharacteristic of the frequency ratio measuring device 7 with respect tothe applied acceleration and the oscillation frequency of the resonantfrequency shift based physical quantity sensor 3. Thus, the nonlinearityof the measurement target signal as the output from the resonantfrequency shift based physical quantity sensor 3 is corrected in such away as to be offset by the “reverse” nonlinearity of the input/outputcharacteristic of the frequency ratio measuring device 7. In thephysical quantity sensor module 1 as a whole, the relation between theacceleration acting on the resonant frequency shift based physicalquantity sensor 3 and the output can be made closer to linearity.

The first low-pass filter 20 and the second low-pass filter 60 arefilters provided on the output side of the frequency delta-sigmamodulator 10 and are not a dedicated circuit or a dedicated mechanismfor correcting nonlinearity. Therefore, the nonlinearity of the physicalquantity sensor can be corrected without increasing the size of thephysical quantity sensor module 1.

Modification

In the first embodiment, the case of changing the setting of the numbersof delays n2 and n3 as the numbers of filter taps of the first low-passfilter 20 is described. However, the setting of the number of delays n1,and the number of delays n4 as the number of filter taps of the secondlow-pass filter 60, can be adjusted, too. In the first low-pass filter20, the input signal is down-sampled by the decimator 32. Therefore, inthe adjustment based on the number of delays n1 of the first delayelement 24 preceding the decimator 32, even with the same number ofdelays, the amount of delay (delay time) of the smoothing timing issmaller than in the adjustment based on the numbers of delays n2 and n3of the second delay element 34 and the third delay element 38. That is,the first low-pass filter 20 has the first delay element 24 having anumber of filter taps that can slightly (finely) adjust the amount ofadjust in the smoothing timing, and the second delay element 34 and thethird delay element 38 having a number of filter taps that can greatly(roughly) adjust the amount of adjust. The first low-pass filter 20 thuscan adjust the smoothing timing, based on a plurality of numbers offilter taps with different levels of roughness/fineness. This makes iteasier to adjust the degree of correction of the measurement targetsignal as the output from the resonant frequency shift based physicalquantity sensor 3.

Second Embodiment

Next, a second embodiment will be described. In the description below,differences from the first embodiment are mainly described. Componentsand elements similar to those of the first embodiment are denoted by thesame reference signs and are not described repeatedly. The secondembodiment is an embodiment of a physical quantity detector, which isthe physical quantity sensor module 1 according to the first embodiment.

FIG. 8 is a cross-sectional view schematically showing an internalstructure of a physical quantity detector 100 according to the secondembodiment. The physical quantity detector 100 has a physical quantitydetection device 200 as the resonant frequency shift based physicalquantity sensor 3 in the first embodiment, an electronic circuit 140,and a package 102 accommodating the physical quantity detection device200 and the electronic circuit 140.

The package 102 has a package base 104 and a lid 106. In the package102, the plate-like lid 106 is coupled to the package base 104 via a lidjoining member 108 in such a way as to cover the space above therecessed package base 104, thus defining an internal space. In thisinternal space, the physical quantity detection device 200 and theelectronic circuit 140 are supported and fixed. The package base 104 canuse, for example, a material such as ceramic, quartz crystal, glass, orsilicon. The lid 106 can use, for example, the same material as thepackage base 104 or a metal such as an alloy of iron (Fe) and nickel(Ni), or stainless steel. The lid joining member 108 can use, forexample, a seam ring, low-melting glass, or inorganic adhesive.

Inside the package base 104, a step part 110 for supporting and fixingthe physical quantity detection device 200 on its upper surface isprovided along an inner wall. On the upper surface of the step part 110,an internal terminal 114 electrically coupled to a fixed part couplingterminal of the physical quantity detection device 200 is provided.

On an outer bottom surface of the package base 104, an external terminal116 used to install the physical quantity detector 100 on an externalmember is provided. The external terminal 116 is electrically coupled tothe internal terminal 114 via an internal wiring, not illustrated. Theinternal terminal 114 and the external terminal 116 are made up of, forexample, a metal film including a metalized layer of tungsten (W) or thelike coated with nickel (Ni), gold (Au) or the like by plating or thelike.

In a bottom part of the package base 104, a penetration hole 120penetrating the package base 104 from the outer bottom surface to theinner bottom surface is formed. In the example shown in FIG. 8, thepenetration hole 120 is in a stepped shape where the hole diameter onthe outer side is greater than the hole diameter on the inner side.Inside the penetration hole 120, a sealing part 122 for airtightlysealing the inside (cavity) of the package 102 is provided. To providethe sealing part 122, for example, an alloy of gold (Au) and germanium(Ge) and a sealant made up of a solder or the like are arranged in thepenetration hole 120, then heated and melted, and subsequentlysolidified. After the lid 106 is joined to the package base 104, thesealant is arranged in the penetration hole 120 in the state where thepressure inside the package 102 is reduced (the degree of vacuum ishigh), and the sealant is then heated and melted, and subsequentlysolidified to provide the sealing part 122. Thus, the inside of thepackage 102 can be airtightly sealed. The inside of the package 102 maybe filled with an inert gas such as nitrogen, helium, or argon.

The electronic circuit 140 provides a drive signal to the physicalquantity detection device 200 via the internal terminal 114 or the like,amplifies a supply frequency outputted from the physical quantitydetection device 200 changing according to the applied physical quantitysuch as acceleration, and outputs the amplified supply frequency tooutside of the physical quantity detector 100 via the external terminal116. On the electronic circuit 140, the frequency ratio measuring device7 and the reference signal oscillator 5 or the like in the firstembodiment are equipped.

FIGS. 9 and 10 are perspective views schematically showing the physicalquantity detection device 200. In FIG. 10, the illustration of a masspart 210 is omitted in order to simplify the explanation. FIG. 11 is aplan view of the physical quantity detection device 200. The physicalquantity detection device 200 has a base part 202 supported on foursides by a support part, a moving part 206 which is coupled by a jointpart 204 extending from the base part 202 and which flexes due to anacceleration on a detection axis, and a physical quantity detectionelement 208.

The physical quantity detection element 208 is, for example, a dualtuning fork-like vibration element formed by patterning a quartz crystalsubstrate sliced out of a quartz crystal ore or the like at apredetermined angle, by photolithography or etching. Of course, thematerial of this element is not limited to quartz crystal. Apiezoelectric material such as lithium tantalate, lithium tetraborate,lithium niobate, lead zirconate titanate, zinc oxide, or aluminumnitride can be used. Also, a semiconductor material such as silicon witha piezoelectric material coating such as zinc oxide or aluminum nitridecan be used.

The physical quantity detection element 208 is formed as a beamextending over the joint part 204. One end side of the beam is fixed tothe base part 202. The other end side is fixed to the moving part 206. Asignal line (not illustrated) is coupled to both ends of the physicalquantity detection element 208 and a predetermined current-voltage isapplied thereto. The physical quantity detection element 208 is thusconfigured to vibrate at a predetermined frequency. When the moving part206 flexes due to an acceleration generated along the measurement axisand causes a stress to act on the beam of the physical quantitydetection element 208, the vibration frequency of the physical quantitydetection element 208 adjusts. Based on the adjust in the vibrationfrequency, a signal corresponding to the acceleration is generated andoutputted as an output signal from the physical quantity detectionelement 208.

Third Embodiment

Next, a third embodiment will be described. In the description below,differences from the first and second embodiments are mainly described.Components and elements similar to those of the first and secondembodiments are denoted by the same reference signs and are notdescribed repeatedly. The third embodiment is an embodiment of anacceleration physical quantity sensor using the physical quantitydetector 100 according to the second embodiment.

FIG. 12 is a cross-sectional view schematically showing an internalstructure of an acceleration physical quantity sensor 300 according tothe third embodiment. The acceleration physical quantity sensor 300 hasan electronic circuit board 310 and an accommodation section 320accommodating the electronic circuit board 310.

In the accommodation section 320, an upper outer case 324 openingdownward is placed on top of a lower outer case 322 and these are sealedtogether, defining an internal space. In the internal space of theaccommodation section 320, the electronic circuit board 310 is supportedand fixed via an inner case 326 and a packing 328.

On the electronic circuit board 310, three physical quantity detectors100 (100 x, 100 y, 100 z) according to the second embodiment of the samespecifications, and an amplifier circuit or the like for amplifying anoutput signal from each physical quantity detector 100 (100 x, 100 y,100 z) are equipped.

The three physical quantity detectors 100 x, 100 y, 100 z equipped onthe electronic circuit board 310 are physical quantity sensors fordetecting an acceleration as a physical quantity and output a signalcorresponding to the acceleration detected along the detection axis. Thethree physical quantity detectors 100 x, 100 y, 100 z are equipped insuch a way that their detection axes are orthogonal to each other. Theacceleration physical quantity sensor 300 is a so-called three-axisacceleration physical quantity sensor which detects an accelerationalong three orthogonal axes.

Fourth Embodiment

Next, a fourth embodiment will be described. In the description below,differences from the first to third embodiments are mainly described.Components and elements similar to those of the first to thirdembodiments are denoted by the same reference signs and are notdescribed repeatedly. The fourth embodiment is an embodiment of aclinometer using the acceleration physical quantity sensor 300 accordingto the third embodiment.

FIG. 13 is a partly cross-sectional side view showing an example of theconfiguration of a clinometer 400 according to the fourth embodiment.The clinometer 400 is a device which outputs a signal corresponding toan angle of inclination at a position where the clinometer 400 isequipped. The clinometer 400 has the acceleration physical quantitysensor 300 according to the third embodiment, a calculator 410 whichcalculates an angle of inclination based on an output signal from theacceleration physical quantity sensor 300, and an external outputterminal 412 which outputs to the outside a signal corresponding to theangle of inclination calculated by the calculator 410, in an internalspace defined by a lower case 402 and an upper case 404. Of course, theclinometer 400 may include another element than these. For example, theclinometer 400 may include a built-in battery, a power supply circuit, awireless device or the like.

The calculator 410 is a circuit which calculates an angle of inclinationbased on an output signal from the acceleration physical quantity sensor300 and outputs a signal corresponding to the angle of inclination. Thecalculator 410 can be implemented, for example, by a general-purpose IC(integrated circuit) or FPGA (field-programmable gate array).

The clinometer 400 according to the fourth embodiment employs theacceleration physical quantity sensor 300 using the physical quantitysensor module 1 according to the first embodiment and therefore canachieve a higher inclination measurement accuracy than the related-artclinometer.

Fifth Embodiment

Next, a fifth embodiment will be described. In the description below,differences from the first to fourth embodiments are mainly described.Components and elements similar to those of the first to fourthembodiments are denoted by the same reference signs and are notdescribed repeatedly. The fifth embodiment is an embodiment of aninertial measurement device using the acceleration physical quantitysensor 300 according to the third embodiment.

FIG. 14 is a partly cross-sectional side view showing an example of theconfiguration of an inertial measurement device 500 according to thefifth embodiment. The inertial measurement device 500 is a deviceequipped on a vehicle and has the acceleration physical quantity sensor300 according to the third embodiment, an angular velocity physicalquantity sensor 510, a circuitry 512 which calculates an attitude of thevehicle based on an output signal from the acceleration physicalquantity sensor 300 and an output signal from the angular velocityphysical quantity sensor 510, and an external output terminal 514 whichoutputs to the outside a signal corresponding to the attitude calculatedby the circuitry 512, in an internal space defined by a lower case 502and an upper case 504. Of course, the inertial measurement device 500may include another element than these. For example, the inertialmeasurement device 500 may include a built-in battery, a power supplycircuit, a wireless device or the like.

The angular velocity physical quantity sensor 510 is basically aso-called three-axis angular velocity physical quantity sensor having aconfiguration similar to the acceleration physical quantity sensor 300and detecting an angular velocity about each of the X-axis, Y-axis, andZ-axis.

The circuitry 512 is implemented, for example, by a general-purpose IC(integrated circuit) or FPGA (field-programmable gate array). Thecircuitry 512 calculates an attitude of the vehicle on which theinertial measurement device 500 is equipped, based on an output signalfrom the acceleration physical quantity sensor 300 and an output signalfrom the angular velocity physical quantity sensor 510, and outputs asignal corresponding to the attitude.

Sixth Embodiment

Next, a sixth embodiment will be described. In the description below,differences from the first to fifth embodiments are mainly described.Components and elements similar to those of the first to fifthembodiments are denoted by the same reference signs and are notdescribed repeatedly. The sixth embodiment is an embodiment of astructure monitoring device using the acceleration physical quantitysensor 300 according to the third embodiment.

FIG. 15 shows an example of the configuration of a structure monitoringdevice 600 according to the sixth embodiment. The structure monitoringdevice 600 has the acceleration physical quantity sensor 300 accordingto the third embodiment equipped in a structure 690 as a monitoringtarget, a transmitter 620 which transmits a detection signal from theacceleration physical quantity sensor 300, a receiver 636 which receivesa signal transmitted from the transmitter 620 via a communicationnetwork 650, and a calculator 632 which calculates an angle ofinclination of the structure 690, based on a signal received by thereceiver 636. The communication network 650 may be wired or wireless.

An acceleration physical quantity sensor unit 610 has the accelerationphysical quantity sensor 300 according to the third embodiment, and thetransmitter 620 including a communication module 622 and an antenna 644to implement functions of a small communication terminal, in an internalspace defined by a lower case 612 and an upper case 614. Of course, thetransmitter 620 may be implemented as a separate communication moduleand antenna from the acceleration physical quantity sensor 300.

The calculator 632 in this embodiment is implemented by an ASIC(application-specific integrated circuit) or FPGA (field-programmablegate array) or the like equipped in a monitoring computer 630. However,the calculator 632 may be a processor such as a CPU (central processingunit), and the processor may arithmetically process a program stored inan IC memory 634, thus implementing a software-based configuration. Themonitoring computer 630 can accept various operation inputs made by anoperator via a keyboard 638 and display the result of arithmeticprocessing on a touch panel 640.

The receiver 636 is implemented by a wired communication device orwireless communication device connected to the communication network650. In this embodiment, the receiver 636 is implemented by acommunication module and antenna for wirelessly communicating with thetransmitter 620. However, the receiver 636 may be implemented as aseparate communication module and antenna from the monitoring computer630.

Seventh Embodiment

Next, a seventh embodiment will be described. In the description below,differences from the first to sixth embodiments are mainly described.Components and elements similar to those of the first to sixthembodiments are denoted by the same reference signs and are notdescribed repeatedly. The seventh embodiment is an embodiment of avehicle using the acceleration physical quantity sensor 300 according tothe third embodiment.

FIG. 16 shows an example of the configuration of a vehicle 700 accordingto the seventh embodiment. While the vehicle 700 in this embodiment isdescribed as a passenger car, the type of vehicle can be adjustedaccording to need. The vehicle 700 may also be a small ship, automatictransporter, on-site transporter car, forklift or the like.

The vehicle 700 has the acceleration physical quantity sensor 300according to the third embodiment, and a controller 710 which controlsat least one of acceleration, braking, and steering, based on adetection signal from the acceleration physical quantity sensor 300. Thevehicle 700 can switch whether to execute automatic driving or not,based on a detection signal from the acceleration physical quantitysensor 300.

The controller 710 is implemented by an in-vehicle computer. Thecontroller 710 is coupled to various physical quantity sensors andcontrollers such as the acceleration physical quantity sensor 300, athrottle controller 712, a brake controller 716, and a steeringcontroller 720 in such a way as to be able to send and receive a signalvia a communication network such as an in-vehicle LAN (local areanetwork). The throttle controller 712 is a device which controls anoutput of an engine 714. The brake controller 716 is a device whichcontrols the operation of a brake 718. The steering controller 720 is adevice which controls the operation of a power steering 722. The type ofthe physical quantity sensor controller coupled to the controller 710 isnot limited to these. Various other types can be set according to need.

The controller 710 causes a built-in arithmetic processor to performarithmetic processing based on a detection signal from the accelerationphysical quantity sensor 300, and determines whether to executeautomatic driving or not. When executing automatic driving, thecontroller 710 transmits a control command signal to at least one of thethrottle controller 712, the brake controller 716, and the steeringcontroller 720, and controls at least one of acceleration, braking, andsteering.

The content of automatic driving can be set according to need. Forexample, when the acceleration detected by the acceleration physicalquantity sensor 300 during cornering reaches a threshold indicating thatthe vehicle is likely to spin out or veer off course, control to preventthe vehicle from spinning out or veering off course may be performed.Also, when the vehicle is parked but the acceleration detected by theacceleration physical quantity sensor 300 reaches a threshold indicatingthat it is likely that the vehicle has abruptly moved forward orbackward due to an operation error, control to completely close thethrottle and force a sudden braking may be performed.

The application of the disclosure is not limited to the aboveembodiments. Various adjusts can be made without departing from thescope and spirit of the disclosure.

What is claimed is:
 1. A physical quantity sensor module comprising: aresonant frequency shift based physical quantity sensor whose frequencyadjusts with a change in physical quantity; a reference signaloscillator which outputs a reference signal; a frequency delta-sigmamodulator which performs frequency delta-sigma modulation of thereference signal, using an operation signal based on a measurementtarget signal outputted from the resonant frequency shift based physicalquantity sensor, and generates a frequency delta-sigma modulated signal;a first filter provided at an output of the frequency delta-sigmamodulator and operating synchronously with the measurement targetsignal; a second filter provided on an output side of the first filterand operating synchronously with the reference signal; and a latchprovided between the first filter and the second filter and operatingsynchronously with the reference signal, wherein the resonant frequencyshift based physical quantity sensor has nonlinearity as acharacteristic of an output signal in response to the change in thephysical quantity.
 2. The physical quantity sensor module according toclaim 1, wherein a cutoff frequency which is a filter characteristicachieved by a combination of the first filter and the second filter islower than a structure resonance frequency of the resonant frequencyshift based physical quantity sensor.
 3. The physical quantity sensormodule according to claim 2, wherein the structure resonance frequencyis a frequency determined based on a structure of the resonant frequencyshift based physical quantity sensor.
 4. The physical quantity sensormodule according to claim 1, wherein the first filter is set to have acharacteristic such that the input/output characteristic is close tolinear in the nonlinearity of the signal under measurement which is theoutput of the resonant frequency shift based physical quantity sensor.5. The physical quantity sensor module according to claim 4, wherein thefirst filter is a smoothing filter configured to adjust a smoothingtiming based on a number of filter taps, and the number of filter tapsis set to a smoothing timing that reduces a vibration rectificationerror of the measurement target signal as the output from the resonantfrequency shift based physical quantity sensor emerging due to thenonlinearity.
 6. The physical quantity sensor module according to claim5, wherein a setting of the number of filter taps is adjustable fromoutside.
 7. The physical quantity sensor module according to claim 5,wherein the first filter is configured to adjust the smoothing timingbased on a plurality of numbers of filter taps with different levels ofroughness/fineness based upon an amount of change in the smoothingtiming.
 8. The physical quantity sensor module according to claim 1,wherein the physical quantity is acceleration.
 9. A clinometercomprising: the physical quantity sensor module according to claim 8;and a calculator which calculates an angle of inclination based on anoutput signal from the physical quantity sensor module.
 10. A structuremonitoring device comprising: the physical quantity sensor moduleaccording to claim 8 equipped on a structure; a transmitter which isequipped on the structure and transmits an output from the physicalquantity sensor module; a receiver which receives a signal transmittedfrom the transmitter; and a calculator which calculates an angle ofinclination of the structure, based on a signal received by thereceiver.